Aristotle METAPHYSICA Book 10 Part 10

Perishable and imperishable

1.
Since contraries are other in form, and the perishable and the imperishable
are contraries (for privation is a determinate incapacity), the perishable
and the imperishable must be different in kind.

2.
Now so far we have spoken of the general terms themselves, so that
it might be thought not to be necessary that every imperishable thing
should be different from every perishable thing in form, just as not
every pale thing is different in form from every dark thing.
For the
same thing can be both, and even at the same time if it is a universal
(e.g. man can be both pale and dark), and if it is an individual it
can still be both; for the same man can be, though not at the same
time, pale and dark. Yet pale is contrary to dark.

3.
But while some contraries belong to certain things by accident (e.g.
both those now mentioned and many others), others cannot, and among
these are 'perishable' and 'imperishable'.
For nothing is by accident
perishable. For what is accidental is capable of not being present,
but perishableness is one of the attributes that belong of necessity
to the things to which they belong; or else one and the same thing
may be perishable and imperishable, if perishableness is capable of
not belonging to it. Perishableness then must either be the essence
or be present in the essence of each perishable thing. The same account
holds good for imperishableness also; for both are attributes which
are present of necessity. The characteristics, then, in respect of
which and in direct consequence of which one thing is perishable and
another imperishable, are opposite, so that the things must be different
in kind.

4.
Evidently, then, there cannot be Forms such as some maintain, for
then one man would be perishable and another imperishable.
Yet the
Forms are said to be the same in form with the individuals and not
merely to have the same name; but things which differ in kind are
farther apart than those which differ in form.